Pm received. Thanks for your quick response and I will paypal you this week.

Btw, it is amazing to me how many guys post up on factory weighted grips and how well they think they are supposed to work. I get a chuckle out of how many times I see your name come up now with links to your research and visual proof of how crummy they actually perform.
Good stuff, and thanks for all the effort you put into this. We are lucky to have this mod available here at HF.

By the way, I just have to do this. Sorry for popping in on your thread but this simply has to be involved here where guys come to understand this mod and do research on why to use it. On one of the 450 threads there was an ongoing discussion about this mod that I was lightly involved with. And much to my amazement HJ jumped in and posted this brilliant response and attempt to describe the forces resident in the tail in an engineers perspective, he put it into a simple language everyone involved could mentally picture. I feel this picture needs to be reiterated here as a function of this thread.

Here was the original question
Quote:
Originally Posted by atunguydI am still trying to get my head around the tennis racquet effect and I recently received some of Heim Joint's bolts for my 450 pro.

My question is that I also have these bearing pitch control links installed:
Can anyone tell me if these would contribute to the tennis racquet effect or not?

And here was the answer.

In order to describe Tennis raquet effect we have to define several things to get everyone on the same page. There is no easy way to do this without graphics so I apologize in advance for the length of this.

Feathering axis: The axis of the blade hub that the blade grips rotate around. The axis that the blade grips rotate on to change thier pitch.

Feathering axis plane: If you sweep the feathering axis by rotating it around the tail shaft axis you generate a plane that is perpendicular to the tail shaft axis.

CG: Center of gravity

TRET tennis raquet effect torque. Torque caused by the centrifugal force generated by tail shaft rotation acting on a mass that can only spin on the feathering axis whose CG is offset from the feathering axis.

Now to try to explain why:
This description assumes a tail blade system is at operating speed where centrifugal force is acting on all the masses that are revolving around the tail shaft axis.

We are going to look at this in steps to build the concept.
First picture a perfectly cylindrical blade grip (no pitch arm, no blade slot, no blade bolt holes, no flats, no blade). the CG of this cylindrical blade grip lies on its axis of rotation which means it also lies on the feathering axis. This means there will be no TRET because there is no offset mass. You could put this cylindrical grip in any angular position and it would stay there because no CG offset = no TRET.

Now add the Pitch arm and bushing and bushing screw to this perfectly cylindrical grip. We just added a mass whose CG is offset from the feathering axis. We can ignore the cylindrical part because it generates no TRET. Why does this offset mass try to get to the feathering axis plane? Since the CG of the offset mass is some distance from the feathering axis, Its distance from the Tail shaft axis will vary as
the blade grip rotates. The longest distance is when the CG of the offset mass lies on the feathering axis plane on either side of the feathering axis (0 degree pitch and 180 degree pitch) The shortest distance is when the CG of the offset mass is 90 degrees to the feathering axis plane (90 deg pitch). Now we remember that this whole mess is spinning and centrifugal force is acting on the offset mass so it is trying to move away form the tail shaft axis. Since the blade grip can rotate around the feathering axis and the offset mass distance to the tail shaft axis changes as it rotates. The mass will move to the position where the offset mass is farthest from the tail rotor axis.
We already know that this is when the CG of the offset mass lies on the feathering axis plane on either side of the feathering axis (0 degree pitch and 180 degree pitch)

The TRET will be:
Zero when the CG of the offset mass lies on the feathering axis plane (0 deg pitch).
It will increase to maximum when the offset mass CG is 45 degrees from the feathering axis (45deg pitch).
It will then decrease to zero when the offset mass CG is 90 degrees from the feathering axis (90deg pitch).
It will increase to maximum again when the offset mass CG is 45 degrees from the feathering axis (135deg pitch).
It will decrease to Zero again when the CG of the offset mass lies on the feathering axis plane (180 deg pitch).
We are obviously only interested in the +/- 45 degree pitch range.

Now add an identical Pitch arm and bushing and bushing screw at 180 degrees to the original. What happens? We just doubled the TRET because both offset mass CG's reach the feathering axis plane at the same time and their individual TRET's add to each other.

Now re-start with our single pitch arm example again and add an identical Pitch arm and bushing and bushing screw at 90 degrees to the original. What happens? We just eliminated all TRET because as one offset mass CG moves toward the feathering axis plane the other offset mass CG is moving away from it. Both TRET's are there but they are equal and opposite which cancels them out totaly. This 90 degree
relationship is key to understanding what things add to Total TRET or subtract from it.

Anything that adds a offset mass that is close to the feathering axis plane at zero pitch is going to increase total TRET. These would include:
The pitch arm of the blade grip.
Anything connected to the end of the pitch arm including a percentage of the mass of the whole pitch link. The flats on the blade grip and the blade bolt holes (since they reduce the mass of the original cylindrical grip 90 degrees to the feathering axis it is the equivalent of adding weight on the featherning axis) The blade itself is predominantly two offset masses on the feathering plane one in front of the feathering axis and one behind.

Anything that adds an offset mass 90 degrees to the feathering axis plane at zero pitch is going to decrease the total TRET. These would include:
The blade slot of the grip.
The blade bolt.
weights built into the grip (if the offset mass CG's are 90 degrees to the pitch arm)
Chinese weights.
If you add too much weight with its CG 90 degrees to the pitch arm at zero pitch you will have situation where the blades try to go to 90 degrees pitch on either side of zero. This is realy bad because it will flutter around zero pitch bouncing off the slop in the whole linkage system.

I hope this helps everyone get thier heads wrapped around TRE so they can look at a tail and Identify what is increasing TRE and what is reducing it.

So the answer to the question about the ball bearing pitch links is yes they will signifigantly increase the Tennis raquet effect. If you have a weighted grip 450 tail and are using those, My T450 SEV2 weights would be a little better since they are heavier than the weights designed for the weighted grips. Or you can do your own and tune them for those links.
HJ

Hey a quick question. I was setting up my new tail using the brand new tarot pro grips on my 450 and am using the SK-720. The tail blades are balanced, new straight shaft. When I spooled it up neutral my tail vibe reading shot up to a .5. Without them it shot down to a .2 using the exact same setup. I ended up putting a new grip assembly (pro again) into place and had exactly the same results. Any ideas?
Thanks
Randy

Hey a quick question. I was setting up my new tail using the brand new tarot pro grips on my 450 and am using the SK-720. The tail blades are balanced, new straight shaft. When I spooled it up neutral my tail vibe reading shot up to a .5. Without them it shot down to a .2 using the exact same setup. I ended up putting a new grip assembly (pro again) into place and had exactly the same results. Any ideas?
Thanks
Randy

Put the whole tail hub and grip assembly (without blades, blade bolts, pitch links) on a straight (balanced) tail shaft on a balancer. If this is out of balance then the grip weight match is off or the bolts/washers holding the grips on need to be matched. If all the weights match perfectly and it is still out of balance then the tail shaft hole in the hub is not centered between shoulers that the bearings mount to. This make the distance to the CG's of everything mouted to the hub different on either side "out of balance".

Put the whole tail hub and grip assembly (without blades, blade bolts, pitch links) on a straight (balanced) tail shaft on a balancer. If this is out of balance then the grip weight match is off or the bolts/washers holding the grips on need to be matched. If all the weights match perfectly and it is still out of balance then the tail shaft hole in the hub is not centered between shoulers that the bearings mount to. This make the distance to the CG's of everything mouted to the hub different on either side "out of balance".

Hope that helps, HJ

Hehe, yes this does help. I saw micro machine marks on the side of the weights that testify how detailed you are in balancing the assembly. So I knew there was an explanation. Looks like I need to spend about half a day in teardown again backtracking through this small mess.
This is just another great wake-up call when using parts that haven't been properly gone through in a professional manner. And for those who think these make very little difference in how much force these add or remove I spun up the tail to speed using the weights without the blades trying to isolate some issues. Even my massive outrage tail servo couldn't push the tail around once it went off center. (I was checking vibe logs). These little things make a profound difference!

As it spins faster, the dough will flatten out. The faster it spins, the more the dough will "want" to flatten out into the plane of rotation to form a flat disc. There's a natural tendency for everything in the spinning pizza dough to stay within the plane of rotation and become a flat spinning disc.

The force that keeps everything in the plane of rotation is the "tennis racquet effect". Maybe it can also be called the "spinning pizza dough effect."

Now apply that to a tail rotor assembly. As it spins, everything will want to move into the plane of rotation to form a flat disc. That tendency increases with higher RPMs.

Force is required to to move anything above or below of the plane of rotation. That includes the pitch arms on the blade grips, as well as the leading and/or trailing edge of the tail rotor blades themselves. The faster it spins, the greater the force needed to move any mass outside the plane of rotation.

Now when you add the Chinese weights, note that they're located outside the plane of rotation compared to the pitch arms. When you spin the tail rotor, they also want to move into the plane of rotation. But the tendency for them to move toward the plane of rotation is counteracted by the force that also keeps the pitch arms from LEAVING the plane of rotation.

It's a dynamic counterbalance to the blade grips.

The end result is the force keeping the blade grips in the plane of rotation are neutralized by the force moving the Chinese weights toward the plane of rotation. This is what makes it a lot easier to move the blade grips, and change the pitch of the tail rotor blades.

It took me a while to come to this conclusion, but after looking at the data provided by the video demo on YouTube, I FINALLY realized that I can use a smaller servo.

When I first built my TRex-450 I installed a Futaba 9650 servo for the tail. Later, I installed the Chinese weight modification, but I kept the Futaba 9650 in place.

About a year later, I finally realize that I can switch to a much smaller servo because the forces to operate the tail is about 1/8 of what it was... duh!

I put in a fast Hitec HS5065MG digital servo, the same servos used for the cyclic. It's 16 grams lighter, less than half the weight of the 9650, and about 1/3 the bulk. It's just as fast as the 9650, or at least according to the tech specifications. And, using a servo programer, I set the center and end points, and also turned the overload protection "on".

After I get the helicopter rebuilt, I'll see if theory is valid in practice. I'm installing a small camera and moving components around to maintain proper balance. So may as well do a few other modifications along the way.

My feeling is that the weights may ease the pressure the servo has to overcome, but you still need a servo that has at least a .07 speed or better. My MksDs95i is a .038. I have two helis equipped with them and one with an Outrage with a .048 speed. The Hs5065mg is only a .11 at 6v. Hardly what I would call a fast tail servo.

I think I definately need a set of these since I have already burned up 1 servo and the ds520 I'm running now with my Quark gets warm after a few min. Not hot after a gyro upgrade but warm. The origional servo failure may hae been from that bad gyro I replaced with the quark but I'd rather invest in a $20 mod then keep spending $50+ on new tal servo's. I have a questiion though. I just bought a new set of grips for my 450 pro but how do I know if they're the weighted ones? I just had my hobbyshop order them and dididn't realize there was diff ones for the Pro?

All pro grips are weighted. But just be aware that the machine work on them varies. I just tossed a new set due to horrific machine work. I had vibes of 13 (skookum 720 is listing severe trouble at 10). And this was weight matched, new shaft, new hub, Ceramic bearings and Kdbb blades. I tossed on an older set of Tarots and my vibes shot down to 0.

Yeah I just tried 3 different sets of EXI 450 pro grips and the holes were drilled at an angle in all three pairs causing binding. And the spacer was thinner in like 2 pairs causing slop in the grip even all the way tightened onto the hub. So I ordered a set of the Align 450 pro's for it and they ad the same problems but not as bad and they are still flyable. I think the vibs ur talking about may be do to these problems. If you hold the grips w/hub in your fingers and like do a circular motion with your wrists you'll notice you can get the hub to start spinning. This is odviously due to the holes being out of true center or at an angle. Also the holes in the tabs for the linkage are off center and that was causing binding on mine. you can see this if you put a screw in it without the linkage. I noticed on mine if I rotated the hub 180 degrees it was way smoother the other way? Anyways, Align parts are way truer then the EXI stuff but still not perfect.

Haha, yeah. I had the same exact problem with the hubs also. Pure garbage. I went through quite a few of them to find one that worked. At $6 a pop it gets crazy. I also tried Exi, Tarot, Align, HK, Sonix, Hdx (both manufactured by the same company), and Ehirobo.
I hate to say this but out of all of them I had the best results with Tarot. I still had to toss the bearings and go with ceramics because the bearings can also cause the same issue with slop. Although I am sure Abec3's would certainly work, I just wanted the tightest bearing tolerances possible. Now I can finally mount the HJ Cw's and get on with this.

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